From e3f3a36e70062c5e54a9b2b66bc66cf98d3ea67e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Motiejus=20Jak=C5=A1tys?= <motiejus@jakstys.lt>
Date: Wed, 19 May 2021 22:57:46 +0300
Subject: [PATCH] wip ST_SimplifyWM

---
 tests.sql |  2 +-
 wm.sql    | 39 +++++++++++++++++++++++++++++++++++++--
 2 files changed, 38 insertions(+), 3 deletions(-)

diff --git a/tests.sql b/tests.sql
index f33ab0b..8560031 100644
--- a/tests.sql
+++ b/tests.sql
@@ -88,8 +88,8 @@ end $$ language plpgsql;
 
 do $$
 declare
-  mutated boolean;
   vcrossings geometry[];
+  mutated boolean;
 begin
   select (self_crossing((select ways from inflections where name='fig6'))).* into vcrossings, mutated;
   perform assert_equals(true, mutated);
diff --git a/wm.sql b/wm.sql
index 0d25b94..93cd0c6 100644
--- a/wm.sql
+++ b/wm.sql
@@ -262,8 +262,43 @@ begin
       end if;
       j = j - prev_length + array_length(bends, 1);
     end loop;
-
   end loop;
-
+end
+$$ language plpgsql;
+
+-- ST_SimplifyWM simplifies a given geometry using Wang & Müller's
+-- "Line Generalization Based on Analysis of Shape Characteristics" algorithm,
+-- 1998.
+drop function if exists ST_SimplifyWM;
+create function ST_SimplifyWM(geometry geom) returns geometry as $$
+declare
+  line geometry;
+  geoms geometry[];
+  bends geometry[];
+  l_type text;
+begin
+  l_type = st_geometrytype(geom);
+  if l_type = 'ST_LineString' then
+    geoms = array(geom);
+  elseif l_type = 'ST_MultiLineString' then
+    geoms = array((select geom from st_dump(geom) order by path[1] desc));
+  else
+    raise 'Unknown geometry type %', l_type;
+  end if;
+
+  foreach line in array geoms loop
+    mutated = true;
+    while mutated loop
+      bends = detect_bends(line);
+      bends = fix_gentle_inflections(line);
+      bends, mutated = self_crossing(bends);
+    end loop;
+  end loop;
+
+  if l_type = 'ST_LineString' then
+    return geoms[1];
+  elseif l_type = 'ST_MultiLineString' then
+    return st_union(geoms);
+  end if;
 end
 $$ language plpgsql;